if a question was merged into another question, the answers will be moved and the source question will be locked.

How long do posts stay locked?

This depends on why it was locked to begin with.

When a moderator locks a post they're required to select how long the lock should remain in place. The options are: 1 hour, 1 day, 1 week, permanent. At the end of this time, the system will automatically unlock it.

When the system locks a post it stays locked indefinitely - only a moderator can unlock it.

A moderator can manually unlock a locked post at any time if they deem it necessary.

When should a post be locked?

As a general rule, temporary locks should be used whenever modifications to a post are causing serious problems on the site. For example:

Permanent locks should almost never be used, with the exception of those imposed by the system itself. There are two exceptions:

An extremely popular question which is now considered inappropriate for the site may be locked for "Historical Significance": this alters the appearance of the question, automatically locks all answers as well, and disables flagging completely. This lock should be reserved for cases where a cherished cultural artifact would otherwise be deleted; do not use it for any other purpose.

A "wiki" is a question whose answers can be edited by low-reputation users, attributed to multiple authors, and do not grant reputation to the original author. They're occasionally useful in cases where information must be compiled by multiple authors (for example, a list of resources or documentation for the site itself); in these cases, locking the question both prevents it from being closed and prevents further answers from being added.